I live near Buford damn on Lanier. Army corps of engineers let the water out once a day. When that happens power output jumps from 7 mw to 120mw. Sirens come on similar to tornado warnings for a few miles down the river, and there are posted warnings not to get in the water of otherwise calm Chatahooche river. Repeat, do not get into water when you hear the sirens. Sit on top 10' kayak. Glad I had a life jacket on, it came handy. Wish I had a helmet. Leg is still banged up.
I did that at my house one time and my then wife acted as if I was leaving kids on a barren island to die. Freakin' nut case.
Whitewater boats are designed to turn quickly, newer boats have flatter bottoms, the older models were rounded bottoms. Turning is more important than straight line tracking. They will turn with the slightest movement. New boaters don't have the skill to paddle straight and will zig zag and sometimes go in circles until they get the required skill. J turn, never heard that term, but it's basically a forward stroke into a small rudder at the end. There's lots of different strokes in WW kayaking, forward, reverse, sweeps, draws, rudders, and all the combinations in between to make the boat go where you want it to go. The forward stroke is all in your torso.
I know I recommended that the OP take a look at the less expensive boats to get started, but I also totally agree that the high-end boats are a lot better than the Wal Mart special. I personally really like Jackson kayaks. Very well designed, very well made, and the outfitting is exceptional. The local "real" kayak store https://aceadventuregear.com/ has a very cool demo program. You pay $20 per day for the demo boat, and you can try out as many as you want. If you buy a boat, they apply all of the demo fees to the purchase. There are so many different brands and sizes that it would be nearly impossible to tell someone which boat was the right one for them. Good luck and have fun!
Yeah, I wouldn’t be too interested in opening/owning a shop, for that reason. It takes a LOT of space to house inventory and the variety is nuts. There’s no way one could ever be competent in everything out there.